Taylor Wilson has a Geiger counter watch on his wrist, a sleek, sporty-looking thing that sounds an alert in response to radiation. As we enter his parents’ garage and approach his precious jumble of electrical equipment, it emits an ominous beep. Wilson is in full flow, explaining the old-fashioned control panel in the corner, and ignores it. “This is one of the original atom smashers,” he says with pride. “It would accelerate particles up to, um, 2.5m volts – so kind of up there, for early nuclear physics work.” He pats the knobs.

It was in this garage that, at the age of 14, Wilson built a working nuclear fusion reactor, bringing the temperature of its plasma core to 580mC – 40 times as hot as the core of the sun. This skinny kid from Arkansas, the son of a Coca-Cola bottler and a yoga instructor, experimented for years, painstakingly acquiring materials, instruments and expertise until he was able to join the elite club of scientists who have created a miniature sun on Earth.

Not long after, Wilson won $50,000 at a science fair, for a device that can detect nuclear materials in cargo containers – a counter-terrorism innovation he later showed to a wowed Barack Obama at a White House-sponsored science fair.

Wilson’s two TED talks (Yup, I Built A Nuclear Fusion Reactor and My Radical Plan For Small Nuclear Fission Reactors) have been viewed almost 4m times. A Hollywood biopic is planned, based on an imminent biography. Meanwhile, corporations have wooed him and the government has offered to buy some of his inventions. Former US under-secretary for energy, Kristina Johnson, told his biographer, Tom Clynes: “I would say someone like him comes along maybe once in a generation. He’s not just smart – he’s cool and articulate. I think he may be the most amazing kid I’ve ever met.”

Seven years on from fusing the atom, the gangly teen with a mop of blond hair is now a gangly 21-year-old with a mop of blond hair, who shuttles between his garage-cum-lab in the family’s home in Reno, Nevada, and other more conventional labs. In addition to figuring out how to intercept dirty bombs, he looks at ways of improving cancer treatment and lowering energy prices – while plotting a hi-tech business empire around the patents.

Nuclear can be used for good or bad. There’s no putting the genie back in the bottle

As we tour his parents’ garage, Wilson shows me what appears to be a collection of nuggets. His watch sounds another alert, but he continues lovingly to detail his inventory. “The first thing I got for my fusion project was a mass spectrometer from an ex-astronaut in Houston, Texas,” he explains. This was a treasure he obtained simply by writing a letter asking for it. He ambles over to a large steel safe, with a yellow and black nuclear hazard sticker on the front. He spins the handle, opens the door and extracts a vial with pale powder in it.

“That’s some yellowcake I made – the famous stuff that Saddam Hussein was supposedly buying from Niger. This is basically the starting point for nuclear, whether it’s a weapons programme or civilian energy production.” He gives the vial a shake. A vision of dodgy dossiers, atomic intrigue and mushroom clouds swims before me, a reverie broken by fresh beeping. “That’ll be the allanite. It’s a rare earth mineral,” Wilson explains. He picks up a dark, knobbly little rock streaked with silver. “It has thorium, a potential nuclear fuel.”

I think now may be a good moment to exit the garage, but the tour is not over. “One of the things people are surprised by is how ubiquitous radiation and radioactivity is,” Wilson says, giving me a reassuring look. “I’m very cautious. I’m actually a bit of a hypochondriac. It’s all about relative risk.”

He paces over to a plump steel tube, elevated to chest level – an object that resembles an industrial vacuum cleaner, and gleams in the gloom. This is the jewel in Wilson’s crown, the reactor he built at 14, and he gives it a tender caress. “This is safer than many things,” he says, gesturing to his Aladdin’s cave of atomic accessories. “For instance, horse riding. People fear radioactivity because it is very mysterious. You want to have respect for it, but not be paralysed by fear.”

***

The Wilson family home is a handsome, hacienda-style house tucked into foothills outside Reno. Unusually for the high desert at this time of year, grey clouds with bellies of rain rumble overhead. Wilson, by contrast, is all sunny smiles. He is still the slightly ethereal figure you see in the TED talks (I have to stop myself from offering him a sandwich), but the handshake is firm, the eye contact good and the energy enviable – even though Wilson has just flown back from a weekend visiting friends in Los Angeles. “I had an hour’s sleep last night. Three hours the night before that,” he says, with a hint of pride.

He does not drink or smoke, is a natty dresser (in suede jacket, skinny tie, jeans and Converse-style trainers) and he is a talker. From the moment we meet until we part hours later, he talks and talks, great billows of words about the origin of his gift and the responsibility it brings; about trying to be normal when he knows he’s special; about Fukushima, nuclear power and climate change; about fame and ego, and seeing his entire life chronicled in a book for all the world to see when he’s barely an adult and still wrestling with how to ask a girl out on a date.

The future feels urgent and mysterious. “My life has been this series of events that I didn’t see coming. It’s both exciting and daunting to know you’re going to be constantly trying to one-up yourself,” he says. “People can have their opinions about what I should do next, but my biggest pressure is internal. I hate resting on laurels. If I burn out, I burn out – but I don’t see that happening. I’ve more ideas than I have time to execute.”

Wilson credits his parents with huge influence, but wavers on the nature versus nurture debate: was he born brilliant or educated into it? “I don’t have an answer. I go back and forth.” The pace of technological change makes predicting his future a fool’s errand, he says. “It’s amazing – amazing – what I can do today that I couldn’t have done if I was born 10 years earlier.” And his ambitions are sky-high: he mentions, among many other plans, bringing electricity and state-of-the-art healthcare to the developing world.

These laudable (and sometimes contradictory) goals have stumped governments, corporations and aid agencies, but for Wilson they are no wishlist. “I want to play major league baseball,” he says. “I want to make a difference.”

‘It’s daunting to know you’re going to be constantly trying to one-up yourself.’ Photograph: Jamie Kingham for the Guardian

Coming from any other 21-year-old this might be filed under hubris, but Wilson is different – as determined as he is smart. “When I said I wanted to build a nuclear fusion reactor in the garage, I think most parents would say no. But my personality is persistent and persuasive.” He shrugs. “It’s important to distinguish IQ from what you do with it.”

The first child born to Kenneth and Tiffany Wilson in May 1994, in Texarkana, Arkansas, there was little reason to anticipate Taylor’s scientific vocation. The American south is better known for its poultry and cotton farming than applied physics. Tiffany ran a yoga studio; Kenneth, a red-meat-loving former college athlete, ran a cola bottling business. How they ended up with a little Einstein remains a mystery. “Neither of us knows a dang thing about science,” Kenneth confesses.

The initial trigger was curiosity. Aged four, Wilson abandoned toy dump trucks to play with real traffic cones and barricades. He stood in front of the house directing traffic, wearing a reflective orange vest, yellow boots and a hard hat.

For his fifth birthday, he demanded a crane – a real one. So Kenneth called a friend who owned a construction company and on the day of the party a six-tonne crane duly arrived, the operator letting Wilson sit in his lap and work the controls.

The crane set a pattern. Tiffany and Kenneth, ignoring friends who muttered about spoiling, resolved to encourage and facilitate the passions of Taylor and his brother Joey, three years younger.

At the age of nine, Taylor announced he would become an astronaut. He set aside books about fantasy and magic to swot up on space exploration. He wrote to astronauts, requesting pictures and autographs, and began building and launching little rockets. At school he gave ebullient talks about space exploration. “Everyone loved watching him, and when he was in the room, he just took control,” Dee Miller, the school’s former head, told his biographer.

As Wilson’s rockets became more elaborate, he detoured into propulsion and making his own fuels. He pinned posters of the periodic table on his wall and pestered his dad for spare parts from the bottling factory. Rockets led to fireworks and (mostly) controlled explosions; sugar was mixed with potassium nitrate to make thunderous bangs that sent mushroom clouds over the yard. The neighbours either freaked out, or came to watch.

For his 10th birthday his grandmother bought him The Radioactive Boy Scout, a book about a teenager in Michigan called David Hahn, who tried to build a nuclear breeder reactor in a back-yard shed in 1994. His experiment ended badly: arrest, disgrace and cleanup workers in hazmat suits. Naturally, Wilson saw the story as a challenge rather than a cautionary tale. His grandmother lived to regret the gift.

All teens can be narcissistic, and when people say you’re Einstein, your identity can get wrapped up in being a whiz-kid

Unlike Hahn, who worked in the shadows to evade a parental ban, Taylor was able to work openly – and under supervision. After becoming obsessed with atoms, the universe’s building blocks, he bought a Geiger counter and started collecting radioactive objects – antique vacuum tubes, figurines, clocks and gadgets from fairs, stores and online – plus a radiation-shielding container made of thick lead. He pushed his parents’ trust and patience to the limit. His biographer recounts an occasion when Tiffany poked her head into the garage and saw her son, in his canary yellow nuclear technician’s coveralls, watching a pool of liquid spreading across the concrete floor.

“Tay, it’s time for supper.”

“I think I’m going to have to clean this up first.”

“That’s not the stuff you said would kill us if it broke open, is it?”

“I don’t think so. Not instantly.”

Wilson was safety conscious, but his explanations about time doses, distance intensities and inverse-square laws baffled his parents. They took advice from university physicists who, after quizzing the teen, concluded he knew what he was doing.

***

Back in the garage in Reno, the adult Taylor Wilson concludes his tour and we wander into the house where his Geiger watch, I gratefully note, stops beeping. The family moved here when he was 14 so he and Joey, a maths prodigy, could attend Davidson Academy, a non-fee-paying school for the brightest of the bright, located on the University of Nevada, Reno campus.

Under the guidance of two mentors in the physics department, Ronald Phaneuf and Bill Brinsmead, Wilson moved his research to the university lab and there pursued his goal of nuclear fusion, charming and cajoling hospitals and other institutions to lend or donate spare parts to supplement the lab’s equipment. He needed to achieve extremely high temperatures and to manage safely the hot gases produced as part of the process. It would involve tens of thousands of electron volts and deadly x-rays: using a fusor was considered too technically challenging even for most doctoral candidates. But in March 2009, using an inertial electrostatic confinement device, Wilson did it. The atoms inside collided and fused, throwing off energy at 1.2m neutrons per second.

The reactor now sits in his garage, but Wilson has on occasion embellished the tale by implying the fusion happened there. Wilson says that even at the moment of triumph, he was mulling his next steps. “I was instantly thinking: what are the applications? What can I do with this?”

Several years later, he received $100,000 from the libertarian-tinged Thiel Fellowship, which funds bright young things for two years – on condition they spurn college during that time and focus on their own projects. His fellowship has now ended but Wilson still has no plans to go to college, preferring instead to work on inventions and to travel, giving talks and visiting friends.

He has proposed building small, self-contained underground nuclear fission reactors that use decommissioned nuclear weapons to fuel power. Another project is to help hospitals irradiate materials for medical isotopes – vital tools that help diagnose cancer but are often too costly for hospitals, especially those in poor countries. Wilson’s innovation holds the promise of dramatically slashing the cost, an initiative he developed in tribute to his grandmother, who died of the disease when he was 11. And then there is the radiation detector designed to intercept terrorist dirty bombs.

Wilson’s achievements are impressive in someone so young, says Steve Cowley, CEO of the UK Atomic Energy Authority and professor of physics at Imperial College London. “What he has achieved is not in itself ground-breaking, but his drive and ingenuity are remarkable. He clearly has a bright future.”

It’s a future that will include nuclear power – something that, despite the “troubling” disaster at Japan’s Fukushima reactor in 2011, Wilson says remains vital when it comes to combating climate change. “Nuclear can be used for good or bad. There’s no putting the genie back in the bottle. My goal is to help prevent the bad and enhance the good.” (Just as well, because he also thinks “there’s something beautiful in a mushroom cloud”.)

We head out for a coffee, Wilson driving us in his parents’ Land Rover. The sun has re-emerged and glints off the city in the valley below. To the east, Elon Musk, the 43-year-old buccaneering entrepreneur behind Tesla and SpaceX, is building a $5bn factory to make lithium-ion batteries for electric cars and home energy storage.

Wilson riffs enthusiastically about electric cars, so I ask if he would work for Musk, whom he has met. He almost groans and shakes his head, then picks his words carefully. “I look up to Elon. That’s hard for me to say. Maybe we both just have big personalities. I have similar ambitions, to do what Elon is doing.” Translation: no matter that Musk is the real-life inspiration for Robert Downey Jr’s Iron Man, Wilson plans to build his own business empire and do things his way.

The cafe has pizza, cookies and cakes, but Wilson demurs. “I’m good on calories for today.” Coffee? He shakes his head. “I tend to avoid caffeine. I don’t really need it. You may have noticed.”

The cashier, a middle-aged woman, clearly recognises him. So, too, do some diners, their eyes following Wilson as we take a table. He got this at the weekend in LA, he says: people know him either from the TED talks, or a much-shared interview he did with CNN in 2012 (Meet Taylor Wilson, Nuclear Prodigy). How does it feel? “I never got into science for the public persona. All that fame stuff, I take it in my stride. I don’t mind it.” Does he like it? A pause. “I don’t dislike it.”

Wilson’s parents have moved back to Arkansas to concentrate on Joey – who, in the shadow of his atomic sibling, was becoming increasingly introverted – leaving him to live alone in the former family home. His strength of character and focus have at times worried and alienated those closest to him. “All teens can be narcissistic, and when you have people telling you every day you’re Einstein, your identity can get wrapped up in being a whiz-kid,” says Clynes, his biographer, speaking from Ann Arbor, Michigan. “Taylor went through some very dark times. I’m not sure if he knew it, but everyone around him did.”

That fear has ebbed and Wilson is now on good terms with loved ones and colleagues, Clynes says. In the transition to adulthood, he matured and discovered some grace and humility – not least in accepting the biography, warts and all. “Reading it hit him hard,” Clynes says. “He was finding out for the first time: wow, I was a jerk. But he got through it and supports the conclusions. How many people would have the maturity to read such things about themselves and consider them accurate?”

‘I’m not very happy when I’m not doing anything. Maybe that’s a sign of neuroses.’ Photograph: Jamie Kingham for the Guardian

What does Wilson make of the accusations of arrogance and narcissism? He squirms before giving a geeky but apparently sincere reply. “It’s something I’m cognisant of. It’s maturity. The experiential gap between 16 and 21 is incredible.” He is not good at foreign languages or sport, he says, failings that give him humility. As does clumsiness in romance. “What makes me nervous? Asking a girl for her number.” He is currently single, he says, without elaborating.

Close friends help keep the ego in check, he adds. “I have my normal friends and go to normal parties. I’m very self-conscious.” Self-conscious because he knows he is not typical of his peers. He abhors downtime, for instance. “I’m not very happy when I’m not doing anything.” He mulls the thought. “Maybe that’s a sign of neuroses.”

There are perks to being the smartest person in the room. But if you’re processing thoughts others may not grasp, do you conceal them and go with the flow – or let rip? For Wilson, this triggers a battle between his newfound humility and his innate ebullience. An unequal contest. “Often when meeting new people, I make an effort to not talk about science and not say who I am,” he says. Wilson sighs and smiles. He’s a man now, but he will always be the boy who built a nuclear reactor in his parents’ garage. Why conceal it?

• The Boy Who Played With Fusion by Tom Clynes is published by Faber & Faber on 2 July at £16.99. To order a copy for £12.99, go to bookshop.theguardian.com or call 0330 333 6846.